Semiconductor Storage Device With Variable Gate Oxide Thickness
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Solution Overview
Problem
Conventional semiconductor storage devices face challenges in achieving high-speed operations while maintaining a stable and compact circuit size, especially when integrated into system LSIs with finer design rules, due to insufficient threshold voltage and increased transistor size requirements.
Innovation Solution
The semiconductor storage device incorporates a control circuit with a gate oxide film of a first thickness, a row decoder circuit with transistors having gate oxide films of varying thicknesses, and a level shift circuit, allowing for high-voltage operation at low voltages and reducing circuit size through optimized transistor configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high breakdown-voltage transistor with a thicker gate oxide film is used in the row decoder circuit, then the reliability is improved, but the transistor size increases and high-speed operation becomes difficult
Solution Approach 1:
The patent applies different gate oxide film thicknesses to different transistor regions within the same circuit. Specifically, the row decoder circuit uses a first gate oxide film thickness optimized for high breakdown voltage and reliability, while the sense circuit uses a second, thinner gate oxide film thickness optimized for high-speed operation. This local differentiation allows each region to operate at its optimal performance point without compromising the other.
Solution Approach 2:
The patent segments the semiconductor device into distinct regions with different electrical characteristics. The row decoder circuit and sense circuit are divided into separate regions, each with independently optimized gate oxide film thicknesses. This segmentation enables the row decoder to handle high-voltage operations reliably while the sense circuit maintains high-speed performance, resolving the contradiction between reliability and speed.
2Reliability
If the gate oxide film thickness is increased for high breakdown voltage, then the reliability is improved, but the circuit area increases
Solution Approach 1:
The patent implements local quality by assigning different gate oxide film thicknesses to specific circuit regions based on their functional requirements. The row decoder circuit, which requires high breakdown voltage, uses a thicker first gate oxide film. The sense circuit, which requires high-speed operation, uses a thinner second gate oxide film. This localized optimization ensures that the thicker film (and its associated area) is only used where absolutely necessary for reliability, minimizing overall circuit area while maintaining required performance.
3Speed
If a thinner gate oxide film is used for high-speed operation, then the operation speed is improved, but the breakdown voltage decreases and reliability deteriorates
Solution Approach 1:
The patent applies local quality by differentiating gate oxide film thickness between circuit regions with different performance requirements. The sense circuit uses a thinner second gate oxide film optimized for high-speed operation, while the row decoder circuit uses a thicker first gate oxide film optimized for high breakdown voltage. This spatial differentiation allows the thinner film to be used only where speed is critical, without compromising the reliability of the high-voltage row decoder operations.
Solution Approach 2:
The patent segments the device into regions with different gate oxide characteristics. The sense circuit region uses a thinner gate oxide film for high-speed read operations, while the row decoder region uses a thicker gate oxide film for reliable high-voltage word line driving. This segmentation resolves the contradiction by allowing each segment to operate in its optimal performance regime.
Data Source
AI summary
In the present invention, a row decoder circuit is made up of a transistor having a first gate oxide film thickness, a transistor having a second gate oxide film thickness, and a transistor having a third gate oxide film thickness. Thus even a control circuit at a lower voltage can drive word lines at high speeds while achieving reliability.